Step 2: The electronics
I made my sensors using 5 SMD IR emiting diodes, 5 SMD phototransistors and 5 1k SMD resistors. Between the phototransistor and the IR I put some black silicone so the IR light would not come directly to the phototransistor. The PCB design is in the archive "line follower.rar". It is made in PROTEUS, but I have a word document including all the PCB designs which can be printed on glossy paper or Press and Peel, and then transfered to the PCB using the method of the iron.
If you don't want to make your own sensor you can buy one from here: http://www.robotshop.com/pololu-qtr-infrared-sensor-array-1.html .
The MICROCONTROLLER PCB:
The "heart" of this robot is an ATMEGA8 microcontroller which gets the information from the sensors and drive the L293D motor controller.
1x 28-pin socket (for ATMEGA8)
1x 14-pin socket (for L293)
1x ATMEGA8 - You can also use an ATMEGA 168 or 328. The program is made in Arduino , so if you have an arduino, you can program the microcontroller on it, then remove it from arduino and insert it in this PCB. Also you can program this microcontroller via the 6 pins with an ISP. You can buy an ATMEGA 328 to program it on your arduino from here: http://www.robotshop.com/sfe-atmega328-with-arduino-bootloader.html
1x 16MHz Crystal
2x 22pF (10-28pF)
1x LM7805 http://www.robotshop.com/lm78m05-voltage-regulator.html
1x Push Button http://www.robotshop.com/sfe-12mm-push-button-switch.html
1x 4.7 uF
1x 1K resistor
1x 33R resistor
1x Break Away Header http://www.robotshop.com/sfe-straight-pin-headers.html
1x Straight Female Header http://www.robotshop.com/straight-female-headers.html
Also you will need one 4 AA battery holder.
Everything you need for making the microcontroller pcb and the sensors PCB is in the "line follower.rar" archive. You will find the PCB design, and the schematics which are made in Proteus, but are also available in the Word document.
Now all you have to do is take the soldering iron and start to solder all the parts.
After you' ve assembled the robot, you need to program the microcontroller. The program is made is Arduino so you can upload it to Arduino and then put the microcontroller in this "motherboard". You also have the HEX file for an ATMEGA8 using 16Mhz crystal.